Rotary engine designs were known as early as 1588, following the development of a rotary engine design by Ramelli. Various rotary engine designs were proposed during the late 1800's following the development of the four stroke, Otto engine cycle in 1876. Rotary engine designs enjoyed popularity in aviation applications at the time of World War I. These engines were primarily air-cooled, with cylinders arranged radially around a crankshaft that was fastened to the fuselage. Various inefficiencies in these designs, however, led to their abandonment after the First World War. Prior to 1910, sources report that more than 2,000 patents had been filed for rotary engine designs. Felix Wankel catalogued over 862 rotary engine configurations, of which more than 500 represented potentially feasible engine designs.
Following Wankel's development of various rotary engine designs, Curtiss-Wright licensed rotary engine technology from Wankel GmbH in 1958. Curtiss-Wright began an aggressive research program into the various applications of rotary engine designs, including automotive, and other applications. Curtiss-Wright, however, did not develop a commercially viable rotary engine design. Instead, in 1984, Curtiss-Wright sold its rotary engine division to John Deere. Deere proceeded to do additional research on stratified charge, rotary engines. As a result of these development efforts, Deere developed a 400 HP rotary engine, in cooperation with Lycoming by the 1980s. Nonetheless, this design required a heavy turbocharger and did not perform well at altitude. (The low atmospheric pressures impaired the turbocharger's performance.) By the late 1980's Lycoming canceled its development work on stratified charge, rotary engine designs.
Numerous engine manufacturers and automotive companies have attempted to develop commercial rotary engine designs including: Curtiss Wright; John Deere Rotary Power International; Mazda; NSU (in Germany); Audi; General Motors; Ford; Daimler-Benz; and Nissan. With the exception of Mazda, each has tried and failed to achieve a commercially successful rotary engine design.
The rotary engine was first used in automotive applications in 1958. Mazda has successfully commercialized various rotary engine designs for automotive applications. The Wankel design, employed by Mazda, is the most fully developed and widely used rotary engine design. Mazda has produced rotary engine units for use in automotive applications. The peak rpm of production Mazda rotary engines is about 8000 rpms. The present inventor believes that the improved rotary engine of the present invention may operate at peak rpm up to about 10,000 rpm, while providing improved engine reliability and efficiency.
In general, most rotary engines involve a design in which the combustion chambers and cylinders rotate with a driven shaft around a fixed control shaft to which the pistons are attached. The pistons rotate around the control shaft. For example, in the Wankel engine, the rotor is designed as an equilateral triangle. The rotor rotates in a specially shaped casing to form three crescent shaped combustion chambers between the convex outer sides of the rotor and the concave inner walls of the casing. Each apex of the rotor is provided with a seal, which separates each combustion chamber from the others. Typically the seals are spring loaded into the edges of the rotor to maintain a pressure-proof seal between the rotor and the casing. The seals maintain continuous sliding contact with the concave inner surface of the casing. As the rotor turns, the combustion chambers progressively increase and decrease in size.
As in a conventional four stroke reciprocating piston engine, a fuel charge enters through an injector system (in a fuel injected design) or an intake port (in a design incorporating a carburetor or port injection). The fuel charge is compressed as the combustion chamber is reduced in size as the rotor turns. The compressed fuel charge is ignited at an appropriate time and expands, providing power to the crankshaft as the combustion chamber expands. The combusted gasses are then exhausted from the engine as the combustion chamber again is reduced in size, forcing the gasses out through an exhaust port.
Unlike a reciprocating piston engine, which typically takes four strokes of the piston (two complete rotations of the crankshaft in a four stroke engine) to accomplish these four stages, each face—combustion chamber—of a typical rotary engine progresses through the strokes of intake, compression, expansion, and exhaust in a single rotation of the crankshaft.
Rotary engine designs offer substantial advantages in terms of simplicity, and reduced weight and size. Prior to the present invention, development of a high performance rotary engine has been prevented by various factors. Although numerous researchers have attempted to improve the performance of rotary engine designs, those efforts of which the present inventor is aware have failed to achieve the performance levels that the Applicant has obtained by the present invention. This situation continues to exist, in spite of the aggressive effort and substantial amount of time and energy devoted to development of improved rotary engine designs throughout this century. Accordingly, there remains a long-felt, and unresolved need for an improved design and method of management of a rotary engine that would achieve the benefits and advantages of the present invention.
There are a number of reasons why prior developers appear to have failed to improve rotary engine design to the levels of the present invention. Although some prior workers recognized that the rotor spins at a different speed than the crankshaft, these prior workers apparently failed to account for this difference in rotation speeds by adjusting the timing of fuel injection and ignition as a function of engine speed. For example, in one embodiment of the present invention based upon a modified Mazda 13B engine, three injector events occur during each revolution of the rotor, one for each chamber. The rotor spins at 2,000 rpm while the crankshaft spins at 6,000 rpm. Yet, in most prior applications, the timing has been driven from the crankshaft as a fixed timing system. Moreover, although the rotational speed of the crankshaft is substantially constant at a given engine rpm, the angular speed of the rotor tip is not. Prior designs have failed, apparently, to account for the effect of these differences on engine injection and ignition timing at different engine rpms.
The recession of the rotor relative to the crankshaft makes it desirable to employ variable injector timing as a function of engine, and rotor, speed. No one, of whom the present inventor is aware, prior to the present invention has achieved direct fuel injection, with fully stratified charge and variable injector timing, to produce the improved performance of the present invention.
Prior attempts to modify injector timing have advanced the injector timing. For example, most prior attempts of which the present inventor is aware advance the injector timing 45° to 65° degrees before top dead center, a point at which there is overlap between combustion chambers. The present inventor has discovered that modifying injection timing as a function of speed, namely, advancing the injector timing when the crankshaft speed increases and retarding timing as when crankshaft speed decreases, improves performance. These advances were not disclosed by prior researchers in the field. The present invention will also improve the performance of direct injection four stroke engines. In particular, the inventor has discovered a method of managing the engine to enhance performance by managing the injector timing—by advancing or retarding injector timing to optimize performance.
The present inventor has found that it is preferable to advance injector timing as a function of engine speed. Specifically, in a preferred embodiment of the present invention, fuel injection timing is modified to begin after the intake means is substantially closed. In an injector of the type known prior to the present invention, the injector pulse rapidly slopes up to full flow, where it is maintained until flow stops abruptly. Fuel injection preferably is stopped prior to the leading edge of the piston coming into proximity with, or passing, the injector. Preferably, flow is stopped prior to the combustion chamber delivering sufficient pressure to cause back flow in the injector. Injector timing preferably is optimized between these two extremes. If injection occurs too early in the cycle, when air flow is not sufficiently turbulent, the fuel is not properly atomized and dispersed. If too late, the face of the piston at its trailing edge is wetted by fuel or fuel is distributed between the trailing edge of one combustion chamber and the leading edge of the next, resulting in loss of efficiency and power. These improvements were not disclosed by prior researchers in the field. The present inventor has found that the timing of fuel injection in a rotary engine has a major impact on engine performance in unexpected ways.
In 1992, King reported that “[i]n general rotary combustion engines have not been able to achieve brake thermal efficiencies as high as that of reciprocating engines. The two primary reasons for this lower efficiency are the rotary's large surface area-to-volume ratio of the combustion chamber and the long cycle time (1.5 times that of the reciprocating engine). Both these factors increase the amount of heat energy lost during combustion. The large surface area-to-volume ratio (a result of the long rectangular shaped chamber) also increases the time required to burn the mixture since the flame has farther to burn and increases the amount of unburned end gas in the combustion chamber. A lean fuel mixture is desirable because it facilitates high thermal efficiency, but at the same time it slows the burn rate which counteracts the benefits of lean burn efficiency.”
King reported that “a method is needed which will allow the engine to operate at lean overall fuel-air ratios (to attain high thermal efficiency) while maintaining, or even increasing, the burning rate of the fuel. Ideally a stratified fuel charge which is rich near the spark plugs and lean around the perimeter of the chamber is desired. This will keep the initial burning rate high due to a rich local mixture around the spark plugs and eliminate the unburned gas near the edges of the chamber.” The solution adopted by King, however, failed to resolve these issues. King, U.S. Pat. No. 5,094,204 for Stratified Charge Injection for Gas-Fueled Rotary Engines (Mar. 10, 1992), which is incorporated herein by reference, discloses a proposed design for a gas-fueled rotary engine. King is directed to a rotary combustion engine in which a gaseous fuel charge is injected into the chamber on compression, after the intake air port closes and early in the compression stroke, to achieve fuel-charge stratification. King reports that this approach is expected to provide the advantages of increased thermal efficiency and volumetric efficiency, reduced exhaust emissions levels, and less tendency to detonate than a homogeneous charged engine.
The approach employed by King teaches away from the present invention, in several ways. King injects only gaseous fuel, which King recognizes displaces intake air, reducing the air/fuel ratio and the apparent size (effective displacement) of the engine. In order to maintain displacement, King allows the fuel to enter the combustion chamber only after the intake port(s) have closed and the chamber is on compression. King injects the gaseous fuel in a manner, at a pressure, and at a location that seeks to avoid displacement of intake air and purportedly achieves charge stratification. Specifically, King reports that he anticipates this result by maintaining the injection pressure at a low pressure, relative to the maximum compression pressure in the combustion chamber, and injecting the fuel charge slowly over a period of time only after the intake valve is closed in order to achieve stratification of the charge. In this manner, King anticipates that the angle and depth of injection of the fuel into the chamber would be controlled. When the compression pressure increases to the level of the fuel supply pressure, injection of fuel is stopped.
King specifically teaches that the “fuel is injected far downstream of the air intake port.” “The air turbulence caused by the intake port has substantially diminished and unidirectional air flow exists in the direction of the rotor rotation.” King '204 patent, Col. 3, at ll. 49-54. King states explicitly, that “the exact location of the gaseous fuel injection is dependent upon the intake port timing of the specific engine, but in general is located in the rotor housing between 270° and 360° rotation of the rotor after compression top dead center, or between 810° and 1,080° rotation of the crankshaft, and in the middle of the width of the housing.” King '204 patent, Col. 3, at ll. 6-11. King maintains the injector pressure well below the pressures achieved during compression and well below the levels at which fuel injectors of the type known in the art operate.
The present invention, in contrast, operates on a wide variety of fuels, including but not limited to gaseous fuels. Rather than reducing the injector pressure, constraining the size and flow rate of the injector, constraining the angle of the injector, and constraining the injector location to immediately before the spark plugs as did King, the present invention employs high- and low-pressure injectors, allows the injector configuration, disposition, and location to be varied depending on the application and desired results, and achieves fully stratified charge with direct fuel injection.
Based upon his experience with the present invention, the present inventor believes that the design disclosed and claimed by King does not perform as disclosed and claimed in the '204 patent. The present inventor believes that an engine made by the teachings of King would not achieve the performance advantages claimed by King, let alone of the present invention. King apparently did not run an actual engine to demonstrate the invention disclosed in King's '204 patent. Rather, King states that “a computer model was created and used to evaluate the present invention” and that the results disclosed were based upon “the modeling data.” King '204 patent, Col. 4, ll. 3-4, and 35. King fails to observe or account for the timing changes observed in the present invention. There is no recognition in King that the rotor varies in speed at different points in its rotation around the crankshaft, nor is there any recognition of the phenomenon observed by the present inventor that in order to achieve the benefits of the present invention, injector timing should be varied at rpm. The present invention overcomes these failures of the prior known designs and methods to produce a high performance (high horsepower and high torque) engine, that achieves superior performance in terms of relatively high and flat horsepower and torque curves, higher fuel economy, lower emissions, improved emissions profile, and improved performance, relative to prior known engine designs and methods of engine management. For example, in laboratory scale testing on the present invention, the present invention has achieved superior performance at fuel efficiencies double that of prior known designs and methods of managing the engine. Further, the present design and method have achieved superior performance under conditions of air to fuel ratio that are considered to be so lean (from about 20:1 to about 60:1) that prior known designs would fail to perform.
The inventor believes that the present invention has achieved several types of results that would have been unexpected by persons of ordinary skill in the art. The invention achieves high performance in a small engine. The invention achieves a high and very desirable horsepower and torque. It does so while maintaining exhaust temperatures at lower levels than would have been anticipated. It achieves these results at an unexpectedly low level of fuel consumption. Emissions are reduced to levels below those that would have been expected for a rotary engine design. Further, the cost of the invention is unexpectedly low relative to prior known designs.
The invention achieves these advantages through a combination of several features, including various combinations of the following features: direct fuel injection; fully stratified charge; variable injector timing; high fuel pump pressures; side port exhaust; variable port timing (intake and/or exhaust); dual exhaust ports; high fuel injector pressures; and injection offset. In addition, various of these features may be employed in differing configurations of the invention, using various fuels, for a variety of end uses.